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Author Topic: Sky Background value in DSS/Baader 3.5nm  (Read 3040 times)

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Offline chris.bailey

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Re: Sky Background value in DSS/Baader 3.5nm
« Reply #15 on: 16:53:36, 16 February, 2016 »
Ian

I'm not too sure all the files made it into that Dropbox folder...there only seem to be 5 lights.

I calibrated the lights manually and it is the master dark that is injecting the noise. The noise in a dark calibrated light frame is an order of magnitude greater than if the dark is dropped (and just using Bias and Flats) but even then the noise is greater in a calibrated light frame compared to one of the raw subs. In fact the Dark frames look very unlike any of my 383L frames, are you sure the cooler was on when they were taken?

Noise is the enemy, particularly on low signal targets as it is signal/noise that governs. As the signal component is small, you don't want the noise to be a governing factor any more than you have to.  As such, you really need the calibration process to add as little as possible to the noise floor and that means good calibration with good master calibration files. That means taking plenty of frames to make them.

I have not used my 10" RC with a 3.5nm Ha filter but I love it on my wider field setup so will certainly be using it when I swap scopes around in a few weeks time though with a larger pixel camera in tow.

As Tom says, would be interesting to see the subs from a brighter target.

Chris
LX200|ZS70|FSQ85|FLT110|Altair DF250RC|EQ6 Pro(Rowan Belt Mod)|ParamountMX
ATIK383L+/EFW2/OAG|Lodestar|Baader 36mm LRGBHaSIIOIII
Starlight Express SXVRH16/ONAG/FW|Lodestar X2|Baader 2" Filters
Starlight Express SXVRH814/ONAG/FW|LodestarX2|Baader 2" Filters
Lunt LS60PTBF1200|DMK41|Quark Chromo
Samyang 135mm f1.8

Offline tomhow

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Re: Sky Background value in DSS/Baader 3.5nm
« Reply #16 on: 17:39:04, 16 February, 2016 »
Cooler was on according to fits header.

Dark frames (and light frames or that matter) seem odd. Very high values. But I haven't seen another 383 dark to compare.
Tak Sky 90, Atik 490, Homemade Mount, OAG, Lodestar

The Curdridge Observatory

Offline chris.bailey

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Re: Sky Background value in DSS/Baader 3.5nm
« Reply #17 on: 18:33:32, 16 February, 2016 »
Cooler was on according to fits header.

Dark frames (and light frames or that matter) seem odd. Very high values. But I haven't seen another 383 dark to compare.

Yes good spot Tom. The Kodak frames are very different to Sony ones and yes they do have a high offset. My 383L darks are pretty clean with obvious bright pixels (in abundance). I only see this sort of noise in my frames when the camera is not getting its full 12 and a bit volts so worth putting a voltmeter on the end of the cable being used to check.
LX200|ZS70|FSQ85|FLT110|Altair DF250RC|EQ6 Pro(Rowan Belt Mod)|ParamountMX
ATIK383L+/EFW2/OAG|Lodestar|Baader 36mm LRGBHaSIIOIII
Starlight Express SXVRH16/ONAG/FW|Lodestar X2|Baader 2" Filters
Starlight Express SXVRH814/ONAG/FW|LodestarX2|Baader 2" Filters
Lunt LS60PTBF1200|DMK41|Quark Chromo
Samyang 135mm f1.8

Offline pomerol

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Re: Sky Background value in DSS/Baader 3.5nm
« Reply #18 on: 18:53:42, 16 February, 2016 »
Tried to send the fits files but it was going to take about 18 hours (I have a slow broadband).
Have put on this link a jpg version of the ic417 tif using the 7nm Ha which only required minor noise removal and had no patern noise/artefacts.
https://www.dropbox.com/sc/79wux6yh396pcpw/AAD9RhsHMX8cWhbPqVwG42TSa
Rgds
Ian S.
Skywatcher Quattro 12 inch F4 on NEQ6 Pro
Skyshed Pod and Pier
Atik383+L
EQMOD / CS5 / Maxim DL5
Baader Ha /O111/S11 Filters
Altair  80mm Guidescope
QHY5 Guider Camera/PHD

Offline tomhow

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Re: Sky Background value in DSS/Baader 3.5nm
« Reply #19 on: 19:01:03, 16 February, 2016 »
Ian - can you post the same thing with the 3.5nm?
Tak Sky 90, Atik 490, Homemade Mount, OAG, Lodestar

The Curdridge Observatory

Offline pomerol

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Re: Sky Background value in DSS/Baader 3.5nm
« Reply #20 on: 19:27:01, 16 February, 2016 »
This is the ic417 through the 3.5nm filter. More noisy than the 7nm but not too bad.
Maybe I should replace my Darks and keep away from the very faint targets?
https://www.dropbox.com/sc/4rdgmiy4wnl6j70/AAB9MR0xM_fc8DJnwXqSEt7ea
Rgds
Ian S.
Skywatcher Quattro 12 inch F4 on NEQ6 Pro
Skyshed Pod and Pier
Atik383+L
EQMOD / CS5 / Maxim DL5
Baader Ha /O111/S11 Filters
Altair  80mm Guidescope
QHY5 Guider Camera/PHD

Offline tomhow

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Re: Sky Background value in DSS/Baader 3.5nm
« Reply #21 on: 19:55:32, 16 February, 2016 »
This is the ic417 through the 3.5nm filter. More noisy than the 7nm but not too bad.
Maybe I should replace my Darks and keep away from the very faint targets?
https://www.dropbox.com/sc/4rdgmiy4wnl6j70/AAB9MR0xM_fc8DJnwXqSEt7ea
Rgds
Ian S.

That's the same image?
Tak Sky 90, Atik 490, Homemade Mount, OAG, Lodestar

The Curdridge Observatory

Offline pomerol

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Re: Sky Background value in DSS/Baader 3.5nm
« Reply #22 on: 21:42:21, 16 February, 2016 »
To remove any confusion (on my part) I have run each again through DSS as previous.Only levels and a little curves, no Noise removal.

https://www.dropbox.com/s/0ot03g1faq9uehl/ic417Ha3.5new1.tif?dl=0
https://www.dropbox.com/s/xb3877iu1f5kjbv/ic417Ha%207nmnew1.tif?dl=0

Rgds
Ian S.
Skywatcher Quattro 12 inch F4 on NEQ6 Pro
Skyshed Pod and Pier
Atik383+L
EQMOD / CS5 / Maxim DL5
Baader Ha /O111/S11 Filters
Altair  80mm Guidescope
QHY5 Guider Camera/PHD

Offline tomhow

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Re: Sky Background value in DSS/Baader 3.5nm
« Reply #23 on: 22:23:34, 16 February, 2016 »
Hmmmm. those are a bit of a puzzle.

I wouldn't expect swapping from one filter to another to have such a dramatic effect. Unless the filter is actually faulty (not unheard of, e.g. poor peak transmission). But I think that is unlikely to be the case here.

One thing I am wondering.... the fit files you uploaded earlier... the light frames of 264 were 900s exposure, but the darks you uploaded are 600s exposure.

Perhaps the stacking software is trying to scale the darks by 1.5x, making a mess of it and vastly increasing the noise in the final stack? What do you think, Chris?

I am inclined in the same way Chris is hinting.. something up with the power to the camera which has nixed the gain in the second set of images. I would another test under the sky with both filters without changing anything else.

Tak Sky 90, Atik 490, Homemade Mount, OAG, Lodestar

The Curdridge Observatory

Offline chris.bailey

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Re: Sky Background value in DSS/Baader 3.5nm
« Reply #24 on: 08:37:57, 17 February, 2016 »
There is definitely something awry with the master dark frame. Its got way more noise (measured in PI) than a corresponding light frame. Power is definitely one thing to look at based on my experience with the 383L. A few other things spring to mind -

Was every frame taken with the same capture software? .fits files have an origin (either top left or bottom left) and I have seen DSS interpret .fits taken with different software wrongly.

There is a new Atik driver package out. Were some of the frames perhaps taken with the old drivers. Its not unheard of for drivers to make subtle differences to the way .fits are written so mixing files from different driver packages can cause issues.

My 383L is not totally light proof (probably the cooler fan vents) so I always do my bias and dark frames in the obsy at night. A slight light leak would hose the dark frames.

If it were me I would do a complete fresh set of calibration frames and go with a minimum of 50 bias (100 is better, 200 better still), 30 darks and 30 flats. As the flats need to be of longer duration than 3 seconds to avoid shutter shadowing, I would also do corresponding flat darks, 30 again, to get as clean a master flat as possible. The bias and dark frames are good for several months leaving only the flats to redo. As I have said before, good calibration is a key with Ha and particularly so with the narrow bandpass of the 3.5nm. It has taken me a while to get the workflow right with my SX814 due to some bias frame issues with that camera.

Chris
LX200|ZS70|FSQ85|FLT110|Altair DF250RC|EQ6 Pro(Rowan Belt Mod)|ParamountMX
ATIK383L+/EFW2/OAG|Lodestar|Baader 36mm LRGBHaSIIOIII
Starlight Express SXVRH16/ONAG/FW|Lodestar X2|Baader 2" Filters
Starlight Express SXVRH814/ONAG/FW|LodestarX2|Baader 2" Filters
Lunt LS60PTBF1200|DMK41|Quark Chromo
Samyang 135mm f1.8

Offline pomerol

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Re: Sky Background value in DSS/Baader 3.5nm
« Reply #25 on: 08:45:04, 17 February, 2016 »
The use of 600 darks was my error as I didn't have 900 in 2x2.Will rectify that and see if anything changes.
Will also check the voltage on the ac adaptor and test both filters (with correct calibration) next time we get a clear night.
Rgds
ian S.
Skywatcher Quattro 12 inch F4 on NEQ6 Pro
Skyshed Pod and Pier
Atik383+L
EQMOD / CS5 / Maxim DL5
Baader Ha /O111/S11 Filters
Altair  80mm Guidescope
QHY5 Guider Camera/PHD

Offline pomerol

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Re: Sky Background value in DSS/Baader 3.5nm
« Reply #26 on: 18:01:28, 17 February, 2016 »
Chris, reference your points, all the frames were taken with the same capture software ( Maxim DL) and using the same drivers.
All the darks and bias were taken in daylight so light leaking could well be the problem.
I am going to delete my dark and bias library and start again in a dark environment, increasing the numbers as per your example.
Will do the above plus check voltage  on the camera and do a 3.5nm/7nm comparison on the same target when we get a clear night.
Many thanks for your input (and Tom).
Rgds
Ian S.
Skywatcher Quattro 12 inch F4 on NEQ6 Pro
Skyshed Pod and Pier
Atik383+L
EQMOD / CS5 / Maxim DL5
Baader Ha /O111/S11 Filters
Altair  80mm Guidescope
QHY5 Guider Camera/PHD

Offline pomerol

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Re: Sky Background value in DSS/Baader 3.5nm
« Reply #27 on: 09:54:50, 19 February, 2016 »
Chris/Tom,
Managed to get 3 hours (bin 2x2) on sh2-261 last night before the trees got in the way with half the time on the 3.5nm and also the 7nm.
Overnight did 45 darks plus 45 new bias.
Just been going through the results and was pleasantly surprised to see no pattern noise and less noise  on the 3.5nm than the 7nm and the image was clearer and sharper.
It is definitely worth me keeping the 3.5 as indications from this result are encouraging.
So as you both suspected, it was all about the calibration, especially the darks which in future I will only ever take in a dark environment and lots of them.
Also checked the input voltage to the camera, it was 12.1 V.
Thanks again for your time and support, it has been a big learning experience for me.
Rgds
Ian S.  :big_clap: :big_clap:
Skywatcher Quattro 12 inch F4 on NEQ6 Pro
Skyshed Pod and Pier
Atik383+L
EQMOD / CS5 / Maxim DL5
Baader Ha /O111/S11 Filters
Altair  80mm Guidescope
QHY5 Guider Camera/PHD

Offline chris.bailey

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Re: Sky Background value in DSS/Baader 3.5nm
« Reply #28 on: 10:22:49, 19 February, 2016 »
Great news Ian. Robust image calibration really is key when doing Ha and especially so as the bandwidth drops. ADU levels tend to be very low, especially in the background so a few counts error is large as a percentage of the total signal. Those error then really show after a stretch.

12.1 volts is a little on the low side in my experience and I think you may find the frames cleaner still if you feed it a little more juice. There was a long thread on the Atik forums about it soon after the 383L came out, started by people who were running them off leisure batteries. They noticed the noise increased as the night wore on and the voltage from the battery reduced. The suggestion from that thread was to avoid voltages below about 12.5volts. The other issue is the voltage can fluctuate slightly as the cooler cycles and adds load. I run mine off 13.8 volts and it is happy as Larry.
LX200|ZS70|FSQ85|FLT110|Altair DF250RC|EQ6 Pro(Rowan Belt Mod)|ParamountMX
ATIK383L+/EFW2/OAG|Lodestar|Baader 36mm LRGBHaSIIOIII
Starlight Express SXVRH16/ONAG/FW|Lodestar X2|Baader 2" Filters
Starlight Express SXVRH814/ONAG/FW|LodestarX2|Baader 2" Filters
Lunt LS60PTBF1200|DMK41|Quark Chromo
Samyang 135mm f1.8

Offline tomhow

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Re: Sky Background value in DSS/Baader 3.5nm
« Reply #29 on: 11:19:30, 19 February, 2016 »
Superb - glad it came good - let's see the images then please! :)
Tak Sky 90, Atik 490, Homemade Mount, OAG, Lodestar

The Curdridge Observatory

 

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